Tigecycline compositions and methods of preparation

ABSTRACT

The present invention relates to novel tigecycline compositions with improved stability in both solid and solution states and processes for making these compositions. These compositions comprise tigecycline, a suitable carbohydrate, and an acid or buffer.

This is a continuation of application Ser. No. 13/011,164, filed Jan.21, 2011, which is a continuation of application Ser. No. 11/374,330,filed on Mar. 13, 2006, and claims the benefit of U.S. provisionalapplication Ser. No. 60/661,030, filed Mar. 14, 2005, all of whichhereby incorporated by reference in their entirety.

The present invention relates to improved tigecycline compositions andmethods for making such compositions. The inventive compositions haveimproved stability in both solid and solution states. The inventivecompositions comprise tigecycline, a suitable carbohydrate, and an acidor buffer. The combination of the suitable carbohydrate and the acid orbuffer reduces tigecycline degradation as explained below. The presentinvention provides advantages over the prior art by providing for stabletigecycline compositions and methods for making such compositions thatachieve stability against both oxidative degradation and epimerization.These compositions are, therefore, more stable when dissolved,lyophilized, reconstituted, and/or diluted than compositions oftigecycline not made according to the invention.

Tigecycline is a known antibiotic in the tetracycline family and achemical analog of minocycline. It may be used as a treatment againstdrug-resistant bacteria, and it has been shown to work where otherantibiotics have failed. For example, it is active againstmethicillin-resistant Staphylococcus aureus, penicillin-resistantStreptococcus pneumoniae, vancomycin-resistant enterococci (D. J.Beidenbach et. al., Diagnostic Microbiology and Infectious Disease40:173-177 (2001); H. W. Boucher et. al., Antimicrobial Agents &Chemotherapy 44:2225-2229 (2000); P. A. Bradford Clin. Microbiol.Newslett. 26:163-168 (2004); D. Milatovic et. al., Antimicrob. AgentsChemother. 47:400-404 (2003); R. Patel et. al., Diagnostic Microbiologyand Infectious Disease 38:177-179 (2000); P. J. Petersen et. al.,Antimicrob. Agents Chemother. 46:2595-2601 (2002); and P. J. Petersenet. al., Antimicrob. Agents Chemother. 43:738-744 (1999), and againstorganisms carrying either of the two major forms of tetracyclineresistance: efflux and ribosomal protection (C. Betriu et. al.,Antimicrob. Agents Chemother. 48:323-325 (2004); T. Hirata et. al.Antimicrob. Agents Chemother. 48:2179-2184 (2004); and P. J. Petersenet. al., Antimicrob. Agents Chemother. 43:738-744 (1999).

Tigecycline has historically been administered intravenously because itexhibits generally poor bioavailability when given orally. Intravenoussolutions have largely been prepared immediately prior to use, e.g.,administration to a patient, from lyophilized powders becausetigecycline degrades in solution principally via oxidation. It would bepreferable as well as desirable to have an intravenous formulation oftigecycline that did not require immediate use and could remain stablein solution for up to 24 hours.

Tigecycline is currently manufactured as a lyophilized powder. Due tothe propensity for tigecycline to degrade, these powders are preparedunder low-oxygen and low-temperature conditions in order to minimizedegradation. Such processing is expensive because it requires specialequipment and handling.

The typical process for preparing these powder compositions involvesdissolving tigecycline in water (compounding) and lyophilizing(freeze-drying) the solution to dryness to form solid cakes of amorphoustigecycline. These cakes are then loaded under nitrogen into stopperedglass vials and shipped to end users such as hospital pharmacies. Priorto being administered to patients, the cakes are reconstituted, often in0.9% saline, to a concentration of, for example, about 10 mg/mL. At thisconcentration, tigecycline degrades rapidly in solution and therefore,must be used without delay. Thus, these reconstituted solutions areimmediately diluted (also known as admixing) to about 1 mg/mL withsaline or other pharmaceutically acceptable diluents into intravenousbags for patient delivery.

In this diluted state, tigecycline is ready for intravenous delivery toa patient. At a concentration of 1 mg/mL, however, tigecycline should beused within 6 hours of dilution. Because intravenous infusions may takeseveral hours, hospital personnel must act quickly so that from the timeadmixture begins to the time the tigecycline dose has been administeredto a patient, not more then 6 hours have elapsed. It would be morepreferred to provide hospital staff with the flexibility and advantagesthat come with longer admixture and reconstitution times so that, forinstance, a hospital pharmacist could prepare a solution the day beforeit is needed to be administered to a patient.

Tigecycline has such a short admixture time and the reconstitution timeis essentially zero because in solution, tigecycline oxidation isrelatively rapid. Under current manufacturing, storage, andadministration conditions, the most prevalent form of degradation is viaoxidation. The reason oxidation is the most prevalent form ofdegradation in previous formulations relates to the chemical structureof tigecycline. It possesses a phenol moiety, and it is well known inthe art of organic chemistry that phenols are particularly prone tooxidation. When tigecycline is dissolved in water prior tolyophilization, the pH is slightly basic (about 7.8). This is higherthan the pKa of the phenolic group on tigecycline. Thus, in both waterand saline solutions, the phenolic group becomes deprotonated and moresusceptible to reaction with oxygen which is why tigecycline compoundingand lyophilization occur under a nitrogen blanket. Accordingly, care toavoid unnecessary exposure to oxygen must be taken by hospital staffduring reconstitution and dilution.

If the pH of the tigecycline solution were less than the pKa of thephenolic group on tigecycline, then oxidation would occur, but to alesser extent. Indeed, it has been observed that tigecycline oxidativedegradation does decrease when the pH is lowered. At low pH, however,another degradative process occurs, epimerization. At lower pHs,epimerization emerges as the most predominant degradation pathway.

Tigecycline differs structurally from its epimer in only one respect.

In tigecycline, the N-dimethyl group at the 4 carbon is cis to theadjacent hydrogen as shown above in formula I, whereas in the epimer,formula II, they are trans to one another in the manner indicated.Although the tigecycline epimer is believed to be non-toxic, it lacksthe anti-bacterial efficacy of tigecycline and is, therefore, anundesirable degradation product.

In the lyophilized state, tigecycline follows the same degradationpathways as in solution, but the rate of degradation is slower. Thus,when tigecycline is lyophilized in water such that the pH is about 7.8,the resulting lyophilized cake exhibits oxidative degradation, albeit ata slower rate than in solution. Similarly, when tigecycline islyophilized in an acidic solution, the primary degradation pathway isepimerization and it also occurs at a slower rate than in solution.

Epimerization is a known degradation pathway in tetracyclines generally,although the rate of degradation may vary depending upon thetetracycline. Comparatively, the epimerization rate of tigecycline isparticularly fast. The tetracycline literature reports several methodsscientists have used to try and minimize epimer formation intetracyclines. In some methods, the formation of calcium, magnesium,zinc or aluminum metal salts with tetracyclines limit epimer formationwhen done at basic pHs in non-aqueous solutions. (Gordon, P. N, StephensJr, C. R., Noseworthy, M. M., Teare, F. W., U.K. Patent No. 901, 107).In other methods, (Tobkes, U.S. Pat. No. 4,038,315) the formation of ametal complex is performed at acidic pH and a stable solid form of thedrug is subsequently prepared.

Other methods for reducing epimer formation include maintaining pHs ofgreater than about 6.0 during processing; avoiding contact withconjugates of weak acids such as formates, acetates, phosphates, orboronates; and avoiding contact with moisture including water-basedsolutions. With regard to moisture protection, Noseworthy and Spiegel(U.S. Pat. No. 3,026,248) and Nash and Haeger, (U.S. Pat. No. 3,219,529)have proposed formulating tetracycline analogs in non-aqueous vehiclesto improve drug stability. However, most of the vehicles included inthese inventions are more appropriate for topical than parenteral use.Tetracycline epimerization is also known to be temperature dependent soproduction and storage of tetracyclines at low temperatures can alsoreduce the rate of epimer formation (Yuen, P. H., Sokoloski, T. D., J.Pharm. Sci. 66: 1648-1650, 1977; Pawelczyk, E., Matlak, B, Pol. J.Pharmacol. Pharm. 34: 409-421, 1982). Several of these methods have beenattempted with tigecycline but none have succeeded in reducing bothepimer formation and oxidative degradation while not introducingadditional degradants. Metal complexation, for example, was found tohave little effect on either epimer formation or degradation generallyat basic pH.

Although the use of phosphate, acetate, and citrate buffers improvesolution state stability, they seem to accelerate degradation oftigecycline in the lyophilized state. Even without a buffer, however,epimerization is a more serious problem with tigecycline than with othertetracyclines such as minocycline.

Others of these methods similarly failed to reduce both epimerizationand oxidative degradation. Although it was found that maintaining a pHof greater than about 6.0 helps reduce epimer formation, as noted above,such conditions lead to greater oxygen sensitivity. With respect tonon-aqueous vehicles, although water is known to accelerate tigecyclinedegradation, it would be impractical to prepare an intravenousmedication using such vehicles.

Whereas it has been determined that processing at temperatures lowerthan room temperature, such as below about 10° C., reduces thetigecycline degradation rate, such processing is expensive and it wouldbe advantageous to use a composition that did not require expensiverefrigeration during processing.

Chinese patent application CN 1390550A discloses that minocycline couldbe combined with an acid to increase the stability toward the oxidativedegradation. It further discloses the use of a caking agent, such asmannitol. This reference says nothing about tigecycline nor does itsuggest that carbohydrates could be used to reduce either oxidation orepimerization for minocycline in reduced pH environments. Indeed,minocycline can be formulated as a hydrochloride salt in intravenousproducts without significant epimerization. In tigecycline hydrochloridesalts, however, significant epimerization occurs. Thus, minocycline andtigecycline possess different epimerization properties.

In another experiment, minocycline was lyophilized at a pH of about 5.0and the lyophilized cake was stored for 20 days at 40° C. and 75%relative humidity. At the end of the 20 days, the cake was analyzed byHPLC. The epimer of minocycline was measured to be present at a level of2.65% by mass. By comparison, when tigecycline was lyophilized at a pHof about 5.0 and the sample stored under the same conditions, but foronly 4 days followed by HPLC analysis, the tigecycline epimer wasmeasured to be at a level of 5.40%, over twice as much even thoughtigecycline was only stressed for ⅕^(th) as long as minocycline. Thus,tigecycline epimerizes much more readily than minocycline, andepimerization is a much more significant problem with tigecycline thanit is for minocycline.

The present invention addresses the various problems and disadvantagesof the prior art by providing for stable compositions of tigecycline insolid and solution form. By lyophilizing an aqueous solution containingtigecycline and a suitable carbohydrate at an acidic pH, we haveprepared tigecycline compositions that are more stable against bothoxidative degradation and epimerization than existing compositions.Because the pH is acidic, oxidative degradation has been minimized.Furthermore, it has been determined that suitable carbohydrates act tostabilize tigecycline against epimer formation at acidic pHs.

Compositions of the invention are more stable in the lyophilized statethan the existing compositions and do not require low-temperature orlow-oxygen processing conditions. Such compositions are also expected topossess reconstitution and admixture stability times greater than thatof the existing compositions. For example, one embodiment of theinvention is stable for 6 hours after reconstitution and stable for anadditional 18 hours after admixture. These extended stability times maketigecycline much easier to use in a hospital environment by providingneeded flexibility to hospital staff when treating patients.

Solid-state compositions of the invention comprise tigecycline, asuitable carbohydrate, and an acid or buffer.

Suitable carbohydrates are those carbohydrates capable of reducingepimer formation in at least one solid form prepared in at least one pHenvironment when compared to a tigecycline solid form prepared at thesame pH environment lacking suitable carbohydrates. In one embodiment,the pH environment ranges from about 3.0 to about 7.0, such as pHsranging from about 4.0 to about 5.0, or from about 4.2 to about 4.8. Inone embodiment, the at least one solid form is chosen from powders andlyophilized cakes of tigecycline. Examples of suitable carbohydratesinclude the anhydrous, hydrated, and solvated forms of compounds such aslactose, mannose, sucrose, and glucose. Suitable carbohydrates includemono and disaccharides e.g. an aldose monosaccharide or a disaccharide,preferably a disaccharide such as lactose and sucrose. Lactose is mostpreferred. Accordingly, suitable carbohydrates may include differentsolid forms. For example, by lactose we include the different solidforms of lactose such as anhydrous lactose, lactose monohydrate or anyother hydrated or solvated form of lactose. Lactose and sucrose aredisaccharides. It is therefore expected that disaccharides as a classwill work according to the invention.

The compositions of the invention include solutions, such as thoseprepared prior to lyophilization, containing tigecycline, a suitablecarbohydrate, and an acid or buffer. In some embodiments of theinvention, the solutions may be stored for several hours prior tolyophilization in order to provide greater manufacturing flexibility.Compositions of the invention further include lyophilized powders orcakes containing tigecycline, a suitable carbohydrate, and an acid orbuffer.

In some embodiments of the invention, the suitable carbohydrate used islactose monohydrate and the molar ratio of tigecycline to lactosemonohydrate in the lyophilized powder or cake is between about 1:0.2 toabout 1:5. Some embodiments have tigecycline to lactose monohydratemolar ratios of between about 1:1.6 to about 1:3.3.

Compositions of the invention also include solutions made from thelyophilized powder or cake by, for example, reconstitution with salineor other pharmaceutically acceptable diluents. Compositions of theinvention further include solutions resulting from diluting thosereconstituted solutions with pharmaceutically acceptable diluents foruse in intravenous bags.

Any carbohydrate capable of reducing epimer formation in the inventionis a suitable carbohydrate and this invention is not limited tocompositions employing those carbohydrates specifically identified.

It is expected that derivatives of sugars, for example, may workaccording to the invention to reduce epimer formation. Thus, to theextent that derivatives of sugars, such as sugar alcohols,glucoseamines, and alkyl esters alone or in combination reduce epimerformation according to the invention, they are suitable carbohydrates.Likewise, other suitable carbohydrates may include higher saccharidessuch as polysaccharides; complex carbohydrates such as hetastarch,dextran; and celluloses such as hydroxypropylmethyl cellulose andhydroxypropyl cellulose. It is further expected that combinations ofcarbohydrates, including monosaccharides and trisaccharides, will besuitable carbohydrates and work to reduce epimer formation according tothe invention.

Acids and buffers of the invention include any pharmaceuticallyacceptable acid or buffer capable of adjusting the pH of atigecycline/suitable carbohydrate solution to between about 3.0 to about7.0, about 4.0 to about 5.0, or about 4.2 to about 4.8. Examples of suchacids include, but are not limited to, hydrochloric acid, including 1.0N HCl, gentisic acid, lactic acid, citric acid, acetic acid, andphosphoric acid. Examples of suitable buffers include succinates.

Compounds of the invention may be prepared via a number of acceptablemethods. The methods described below are exemplary and not meant tolimit the invention.

In one method of the invention, tigecycline is dissolved in water toform a solution. The pH of the solution is subsequently lowered byaddition of an acid or buffer. A suitable carbohydrate is then dissolvedin the solution and the solution is lyophilized to dryness to form alyophilized powder or cake.

Tigecycline may be blended with a suitable carbohydrate and dissolved inwater. After the pH of the solution is adjusted so that it is acidic,the solution may then be lyophilized to dryness to form a lyophilizedpowder or cake.

Lyophilization of solutions of the invention may be accomplished by anypharmaceutically acceptable means. Once lyophilized, compositions of theinvention may be stored under an inert gas, such as nitrogen, to furtherslow the degradation process, but, unlike the current tigecyclinecomposition, such low oxygen environments are not necessary for theinvention.

When tigecycline is combined with a suitable carbohydrate, anysolid-state form of tigecycline that is sufficiently soluble in watermay be used. Such solid-state forms include crystalline tigecyclinepolymorphs, amorphous forms, and salts.

Additionally, when preparing tigecycline solutions of the invention forlyophilization, one adds sufficient acid or buffer to the aqueoussolution containing tigecycline to obtain a pH from about 3.0 and about7.0 including from about 4.0 to about 5.0 and from about 4.2 to about4.8.

The compositions of the invention may be prepared for single-dosage use.In this embodiment, the solutions of the invention are lyophilized inindividual vials, such as 20 ml vials. Upon lyophilization, the vialsare stoppered with any pharmaceutically acceptable stopper. Thestoppered vials are then shipped for use.

When needed, the vials can be reconstituted by adding sufficient diluentto achieve the desired concentration of tigecycline. The concentrationof reconstituted solutions may be easily determined by those of ordinaryskilled in the art. Any pharmaceutically acceptable diluent may be used.Examples of such diluents include water, saline, such as 0.9% saline,Lactated Ringer's Injection solution and dextrose solutions including 5%dextrose (D5W).

Reconstituted solutions of the invention may then be stored in areconstituted state, unlike current compositions, prior to admixture.Admixture can occur, for example, in an intravenous bag. To prepare anadmixture, sufficient reconstituted solution is mixed in an intravenousbag containing a pharmaceutically acceptable diluent such as salinesolution or dextrose solution such as D5W. The concentration ofadmixtures may be easily determined by those of ordinary skill in theart. Admixture times for compositions of the invention can be muchlonger than those of the existing composition. Once admixed, thetigecycline solution is ready for patient administration. The admixturemay be administered alone or together with another pharmaceutical agentor composition.

The following six examples illustrate various embodiments of theinvention and are not intended to limit the invention in any way. Eachexample details several experiments where tigecycline was dissolved witha carbohydrate in aqueous acidic solution, lyophilized, and analyzed fordegradation products by HPLC. The HPLC conditions for each example wereessentially the same. The tables accompanying the examples reflect theresults of the HPLC data which show the oxidative degradation productsidentified in the tables as relative retention times (RRT) 0.50/MW 601and RRT 0.55/MW 583, the epimer (RRT 0.74/MW 585), and the total amountof tigecycline present under a variety of conditions (identified as“Tigecycline” in the tables”). In many instances, after the solutionswere lyophilized, they were placed under accelerated stabilityconditions of 40° C. and 75% relative humidity. These conditions areindustry standards used for simulating the effect of long-term storageunder normal shelf conditions.

In example 1, solutions of tigecycline, lactose, and 1.0 N HCl werelyophilized and the resulting cakes were placed in stability chambers at40° C. and 75% relative humidity for 25 days. At the end of the 25 days,the cakes were analyzed by HPLC to identify degradation products.

A similar experiment is detailed in Example 2a. There, the lyophilizedcakes were analyzed by HPLC after being stored for 39 days at 40° C. and75% relative humidity. Sample cakes from two of the experiments werereconstituted in D5W (5% dextrose) and samples from the remaining cakeswere reconstituted in saline immediately prior to HPLC analysis.

In experiment 2b, after the lyophilized cakes were stressed as per theconditions in example 2a, several of the cakes were reconstituted in0.9% saline and kept in solution for 6 hours. Others were reconstitutedin dextrose. At the end of the 6 hour period, some of these solutionsamples, as identified in table 2b, were tested by HPLC.

Example 2c illustrates a stability test on admixed solutions. In thesesolutions, the reconstituted solutions of example 2b were held for 6hours at about 10 mg/mL and then diluted to about 1 mg/mL, the typicalintravenous concentration for tigecycline, and held for 18 hours priorto analysis by HPLC (table 2c).

In example 3, gentisic acid, rather than hydrochloric acid, was used toreduce the pH of the pre-lyophilized solutions of tigecycline. Oncelyophilized, the cakes were stressed at 45° C. and 75% relative humidityfor 48 days and then analyzed by HPLC.

The samples of example 4 show the effects of changing from lactose toother carbohydrates on epimer formation and tigecycline recovery whenmaking the pre-lyophilized tigecycline solutions. In each of examples4a, 4b, and 4c, the indicated solutions were prepared and lyophilized.Each cake was stressed according to the parameters provided in examples4a-4-c, taken into solution, and analyzed by HPLC.

Hold time, the time in between compounding and lyophilization, and orderof tigecycline and lactose addition were studied as factors in epimerformation and tigecycline recovery in example 5. Once the cakes werelyophilized, they were stressed at 40° C. and 75% relative humidity for48 days prior to HPLC analysis. Summaries of the HPLC data appear intable 5.

The ratio of lactose to tigecycline was varied in the experiments inexample 6. When preparing the solutions to be lyophilized, varyingratios of lactose to tigecycline were employed. The mass ratios arereported in the first column of table 6. The solutions, which each had apH of about 5.0, were subsequently lyophilized to dryness and theresulting cakes were stressed at 40° C. and 75% relative humidity for 20days and analyzed by HPLC.

EXAMPLE 1

Tigecycline (1880 mg) was dissolved in 75 ml of Milli-Q water to form abulk solution. An aliquot from this bulk solution containingapproximately 100 mg of tigecycline was dissolved into a 20 ml vialcontaining 200 mg of lactose monohydrate. Another aliquot of the bulksolution containing approximately 100 mg of tigecycline was placed intoan empty 20 ml sample vial. No pH adjustment was made to either of thesetwo solutions. The solutions were subsequently lyophilized to dryness.

The pH of the remaining bulk solution was lowered to about 6.0 with theaddition of 1.0N HCl. Once a pH of about 6.0 was obtained, an aliquotfrom the bulk solution containing about 100 mg of tigecycline wasdissolved into a 20 ml sample vial containing about 200 mg of lactosemonohydrate and the resulting solution was lyophilized to dryness. Theremaining bulk solution was treated with 1.0N HCl until a pH of about5.5 was obtained at which point 100 mg of tigecycline from the bulksolution was transferred into a 20 ml vial containing 200 mg of lactosemonohydrate. After dissolution, the solution was lyophilized to dryness.Similarly, 20 ml sample vials containing solutions of about 100 mg oftigecycline and about 200 mg of lactose were prepared at pHs of about5.0 and about 4.5. Another solution sample was prepared at about pH 4.5without any lactose. In each case, the solutions were subsequentlylyophilized to dryness. All lyophilizations were done on solutionsfrozen at −70° C. by dry ice with acetone.

The lyophilized samples were placed in a 40° C./75% RH chamber for 25days. Afterwards, the samples were analyzed by HPLC and a summary of theresults appears below in table 1, which reflects the major degradationproducts for each cake that was tested. The sum total of the 6 majordegradation products listed in the tables does not equal 100% becausenot all degradation products are listed in the table. Of the 7 cakestested in example 1, 5 were compositions of the invention and the firsttwo (tigecycline alone without pH adjustment and tigecycline pluslactose without pH adjustment) were controls.

The advantages of the compositions of the invention are apparent fromthis example. For instance, in the composition prepared without lactoseat a pH of about 4.5, only 74.10% tigecycline was detected whereas theepimer was present in an amount of 23.51%. By comparison, the pH 4.5sample with lactose contained only 2.53% epimer and had a tigecyclinecontent of 97.17%.

TABLE 1 Epi- mer Tigency- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 Tigecycline 0.57 2.15 6.50 2.50 1.72 80.59 only(no pH adjustment) Tigecycline + 0.61 0.48 1.05 0.71 1.05 91.95 lactose(no pH adjustment) pH 6.0 + lactose 0.04 0.15 2.56 0.04 0.12 96.83 pH5.5 + lactose 0.01 0.11 2.54 0.01 0.04 97.07 pH 5.0 + lactose 0.01 0.042.43 ND 0.02 97.27 pH 4.5 (no 0.11 0.21 23.51 0.14 0.16 74.10 lactose)pH 4.5 + lactose 0.01 0.05 2.53 ND 0.01 97.17 ND = Not detected; MW ismolecular weight; RRT means relative retention time to tigecycline peak.

EXAMPLE 2

2a. Tigecycline (1700 mg) was dissolved in 85 ml of Milli-0 water toform a bulk solution. Solutions containing about 100 mg of tigecyclineand about 200 mg of lactose monohydrate were prepared at pHs of about5.2, 5.0, 4.8, and 3.0 in the same manner that tigecycline/lactose/HClsolutions were prepared in example 1. A solution of tigecycline andlactose at pH of about 4.5 was prepared by adding 1.0 N NaOH to the bulksolution at pH 3.0 followed by dissolving an aliquot of bulk solutioncontaining about 100 mg of tigecycline into a 20 ml vial containingabout 200 mg of lactose monohydrate. All samples were lyophilized(frozen at −50° C. by freeze dryers from AdVantage/Virtis) to dryness.The lyophilized samples were placed in a 40° C./75% RH chamber for 39days and sub-sampled and analyzed by HPLC. The data are shown in table2a.

2b. At the end of 39 days, the lyophilized cakes of Example 2a werereconstituted with 0.9% NaCl to a concentration of 10 mg/ml oftigecycline and kept at room temperature for 6 hours. Separate aliquotsof the solutions at pH of about 5.0 and about 4.5 were reconstitutedwith 5% Dextrose, instead of saline, to a concentration of about 10mg/ml and kept at room temperature for 6 hours. Each of the solutionswas then analyzed by HPLC, and the results are shown in Table 2b.

The data show that the compositions of the invention protect againstepimer formation in reconstituted solutions for 6 hours. Indeed, themaximum epimer content of any one of these examples was only 2.45%,whereas the minimum tigecycline content was 97.1%. In one embodiment,where the pH was about 4.5 and the diluent was saline, at the end of the6 hour reconstitution period, only 1.60% of epimer was present. In thatembodiment, the amount of tigecycline was measured to be 98.15%, which,in some applications, may be of sufficient purity for hospital use.

2c. Admixture solutions of tigecycline (at 1 mg/ml) were made bydiluting the reconstituted solution (from example 2b) with 0.9% NaCl or5% Dextrose depending upon which diluent was used for reconstitution.The solutions were then kept at room temperature for 18 hours andanalyzed by HPLC. The results are summarized in Table 2c.

The sample at about pH 4.5 with lactose and without dextrose had itsepimer concentration increase from 1.60% to only 1.80% on going fromreconstitution to admixture whereas the overall tigecycline contentdecreased only slightly for that sample from 98.15% to 97.97%. Theseresults on the about pH 4.5 sample illustrate that that sample issufficiently stable after the lyophilized cake is stored underaccelerated stability conditions for 39 days followed by 6 hours ofreconstitution and 18 hours of admixture.

TABLE 2a Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 pH 5.2 + lactose 0.01 0.08 2.21 ND ND 97.58 pH5.0 + lactose 0.01 0.07 2.20 ND 0.01 97.57 pH 5.0 + lactose 0.01 0.082.21 ND 0.01 97.38 in 5% dextrose pH 4.8 + lactose 0.01 0.02 2.15 ND ND97.63 pH 4.5 + lactose 0.01 0.03 1.37 ND 0.01 98.42 pH 4.5 + lactose0.01 0.02 1.35 ND ND 98.23 in 5% dextrose pH 3.0 + lactose 0.01 0.021.34 ND ND 98.49

TABLE 2b Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 pH 5.2 + lactose 0.01 0.12 2.31 0.01 0.04 97.37pH 5.0 + lactose 0.01 0.10 2.37 ND 0.03 97.33 pH 5.0 + lactose 0.01 0.102.45 0.01 0.03 97.10 in 5% dextrose pH 4.8 + lactose 0.01 0.09 2.32 ND0.02 97.41 pH 4.5 + lactose 0.01 0.09 1.60 0.01 0.02 98.15 pH 4.5 +lactose 0.01 0.08 1.65 ND 0.01 97.96 in 5% dextrose pH 3.0 + lactose0.01 0.06 2.10 ND ND 97.70

TABLE 2c Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 pH 5.2 + lactose 0.01 0.05 2.49 0.01 0.09 97.11pH 5.0 + lactose 0.01 0.06 2.57 0.01 0.06 97.09 pH 5.0 + lactose 0.020.05 2.80 0.01 0.06 96.66 in 5% dextrose pH 4.8 + lactose 0.02 0.04 2.520.01 0.04 97.19 pH 4.5 + lactose 0.01 0.03 1.80 ND 0.03 97.97 pH 4.5 +lactose 0.02 0.02 2.02 ND 0.02 97.56 in 5% dextrose pH 3.0 + lactose0.01 0.04 2.72 ND ND 97.13

EXAMPLE 3

Tigecycline (700 mg) was dissolved in 28 ml of Milli-Q water to form abulk solution. An aliquot of the bulk solution containing about 100 mgof tigecycline was loaded into a 20 ml vial as control sample. Solutionsamples of tigecycline, lactose, and an acid were prepared at pHs ofabout 5.8, 5.1, and 4.5 according to the methods of example 1 exceptthat gentisic acid was used to lower the pH of the bulk solution ratherthan 1.0 N HCl. An additional two samples of tigecycline solutionswithout lactose were prepared, one at a pH of about 5.1 and another at apH of about 4.5. All of the solutions were frozen at −70° C. (by dry icewith acetone) and lyophilized to dryness. The lyophilized samples wereplaced in a 40° C./75% RH chamber for 48 days and analyzed by HPLC. Thedata are summarized in Table 3 and show that this composition worksaccording to the invention to reduce degradation.

TABLE 3 Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 Control 0.37 2.17 7.37 1.50 1.47 81.13 pH 4.5 nolactose 0.02 0.05 28.11 0.04 0.02 71.37 pH 4.5 + lactose 0.01 0.02 6.32ND ND 93.42 pH 5.1 no lactose 0.05 0.10 20.90 0.10 0.08 77.87 pH 5.1 +lactose 0.01 0.02 3.94 ND 0.02 95.82 pH 5.8 no lactose 0.04 0.13 17.380.21 0.21 81.31

EXAMPLE 4

4a. Tigecycline (1600 mg) was dissolved in 64 ml of Milli-Q water toform a bulk solution and two samples from the solution, each containingabout 100 mg of tigecycline, were loaded into two separate sample 20 mlsample vials containing 160 mg of lactose monohydrate and 160 mgmannitol respectively. A third sample containing about 100 mg oftigecycline from the bulk solution was loaded into a blank 20 ml vial.The pH of the remainder of the bulk solution was sequentially adjustedwith 1.0N HCl to about 7.0, 6.5, and 6.0 as per the procedure outlinedin example 1. Sample solutions each containing about 100 mg tigecyclinewere loaded into 20 ml vials containing 160 mg of lactose monohydrate,160 mg of mannitol, or neither at each pH value. The resulting solutionswere lyophilized (frozen at −70° C. by dry ice with acetone) to dryness.The lyophilized samples were placed in a 40° C. oven for 70 hours andthen analyzed by HPLC. The data are summarized in table 4a.

4b. Tigecycline (1800 mg) was dissolved in 72 ml of Milli-Q water toform a bulk solution. Aliquots from the bulk solution containing about100 mg of tigecycline were loaded into three separate 20 ml vialscontaining about 200 mg of lactose monohydrate, fructose, and sucroserespectively. The pH of the bulk solution was sequentially adjusted with1.0N HCl to about 6.0 and 5.4 according to the procedure outlined inexample 1. At each pH value, aliquots of solution containing about 100mg of tigecycline were taken into 20 ml vials containing 200 mg of oneof the following carbohydrates:

lactose monohydrate, fructose, or sucrose and dissolved. Solutionswithout carbohydrates were also prepared at each pH value. The solutionswere lyophilized (frozen at −70° C. by dry ice with acetone) to dryness.The lyophilized samples were placed in a 40° C. oven for 89 hours andanalyzed by HPLC. The results are summarized in Table 4b.

4c. Tigecycline (1000 mg) was dissolved in 50 ml of Milli-Q water toform a bulk solution. The pH of the bulk solution was adjusted with 1.0NHCl to about 5.0. Four aliquots of bulk solution, each containing about100 mg of tigecycline, were loaded into 20 ml vials containing about 200mg of glucose, mannose, ribose, and xylose respectively and dissolved. Afifth aliquot of bulk solution containing about 100 mg of tigecyclinewas loaded into a 20 ml vial containing about 125 mg of threose anddissolved. All five solutions were lyophilized (frozen at −50° C. byfreeze dryers from AdVantage/Virtis) to dryness. The lyophilized sampleswere placed in a 25° C./60% RH chamber for 42 days and analyzed by HPLC.The results are summarized in table 4c. Data in tables 4a-4-c are meantto illustrate the effect of suitable carbohydrates such as lactose onthe invention.

TABLE 4a Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 Tigecycline only 0.03 0.07 1.08 ND 0.07 98.51 pH7.0 0.03 0.06 1.15 0.02 0.09 98.35 pH 6.5 0.03 0.06 1.73 0.02 0.09 97.78pH 6.0 0.02 0.06 2.69 0.02 0.08 96.82 Tigecycline + 0.03 0.10 0.89 ND0.07 98.33 lactose pH 7.0 + lactose 0.03 0.08 0.94 ND 0.06 98.45 pH6.5 + lactose 0.02 0.05 0.91 ND NA 98.50 pH 6.0 + lactose ND 0.04 0.90ND NA 98.54 Tigecycline + 0.05 0.13 1.40 ND 0.14 97.69 mannitol pH 7.0 +mannitol 0.05 0.11 1.80 ND 0.12 97.45 pH 6.5 + mannitol 0.03 0.08 2.28ND 0.08 96.98 pH 6.0 + mannitol 0.02 0.06 2.56 ND 0.07 96.82

TABLE 4b Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 Tigecycline only 0.04 0.12 1.06 0.04 0.12 98.39pH 6.0 0.03 0.09 2.72 0.03 0.08 96.90 pH 6.0 + lactose 0.01 0.04 0.97 ND0.03 98.76 pH 5.4 + lactose 0.01 0.06 1.01 0.01 0.03 98.71 pH 6.0 +fructose 0.04 0.09 17.70 0.02 0.02 81.92 pH 6.0 + sucrose 0.01 0.08 1.380.02 0.03 98.32

TABLE 4c Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 pH 5.0 + glucose 0.01 0.06 1.02 ND 0.01 98.81 pH5.0 + mannose 0.01 0.06 1.23 ND ND 98.60 pH 5.0 + ribose 0.44 0.02 33.30ND 0.01 65.94 pH 5.0 + xylose 0.02 0.09 18.05 ND ND 81.68 pH 5.0 +threose 0.91 3.41 7.00 0.07 0.79 22.85

EXAMPLE 5

5a. Tigecycline (1000 mg) was dissolved in 40 ml of Milli-Q water toform a bulk solution. The pH of the bulk solution was adjusted with 1.0NHCl to about 5.0. At that pH, two aliquots of the bulk solution, eachcontaining about 100 mg tigecycline, were loaded separately into two 20ml vials each containing about 200 mg lactose monohydrate. One samplewas frozen immediately at −70° C. (by dry ice with acetone), and theother sample was kept at room temperature for 5 hours before freezing.Frozen samples were subsequently lyophilized to dryness. The lyophilizedsamples were placed in a 40° C./75% RH chamber for 48 days and analyzedby HPLC. The results are summarized in Table 5 as the “A” samples.

5b. Lactose monohydrate (750 mg) was dissolved in 15 ml of Milli-Qwater. Tigecycline (375 mg) was added to this solution and the pH wasadjusted to about 5.0 with 1.0N HCl. At this pH, two aliquots from thesolution, each containing about 100 mg of tigecycline and about 200 mgof lactose monohydrate, were loaded into two 20 ml vials respectively.The solution in one sample vial was frozen immediately at −70° C. (bydry ice with acetone). The solution in the other sample was kept at roomtemperature for 5 hours before freezing. Frozen samples were lyophilizedto dryness. The lyophilized samples were placed in a 40° C./75% RHchamber for 48 days and analyzed by HPLC. The results are summarized inTable 5 as the “B” samples. The “A” and “B” data illustrate compositionsof the invention reducing degradation products.

TABLE 5 Epi- mer Tigecy- RRT 0.5 0.55 0.74 1.25 1.67 cline Sample ID MW601 583 585 528 556 585 A (lactose dissolved 0.01 0.02 3.18 0.01 0.0296.57 in tigecycline) B (tigecycline dis- 0.00 0.02 3.32 ND 0.01 96.43solved in lactose) A left in RT for 0.01 0.03 5.67 0.02 0.02 94.03 5 hrsbefore freeze B left in RT for 0.01 0.02 3.82 ND 0.02 95.86 5 hrs beforefreeze

EXAMPLE 6

6a. Tigecycline (1700 mg) was dissolved in 85 ml of Milli-Q water toform a bulk solution. The pH of the bulk solution was adjusted to about5.0 with 1.0N HCl. Four aliquots of the bulk solution, each containingabout 100 mg tigecycline, were loaded separately into four 20 ml vialscontaining about 50, 100, 200, and 300 mg of lactose monohydraterespectively. Once the lactose completely dissolved, the samples werelyophilized (frozen at −50° C. by freeze dryers from AdVantage/Virtis)to dryness. The lyophilized samples were placed in a 40° C. 75% RHchamber for 4 days and analyzed by HPLC. The results are summarized inTable 6a and give examples of compositions of the invention.

6b. Tigecycline (400 mg) was dissolved in 20 ml of Milli-Q water to forma bulk solution. The pH of the bulk solution was adjusted to about 5.0with 1.0N HCl. Three aliquots of the bulk solution, each containingabout 100 mg tigecycline, were loaded separately into three 20 ml vialscontaining 15, 31, and 62 mg lactose monohydrate respectively. Upondissolution, the samples were lyophilized (frozen at −50° C. by freezedryers from AdVantage/Virtis) to dryness. The lyophilized samples wereplaced in a 40° C./75% RH chamber for 20 days and analyzed by HPLC. Theresults are summarized in Table 6b and show compositions of theinvention.

TABLE 6a Epi- mer Tigecy- Sample ID RRT 0.5 0.55 0.74 1.25 1.67 cline(molar ratio) MW 601 583 585 528 556 585 pH 5.0 + lactose ND 0.04 1.01ND ND 98.53 50 mg (1:0.81) pH 5.0 + lactose ND 0.04 0.82 ND ND 98.73 100mg (1:1.62) pH 5.0 + lactose ND 0.04 0.82 ND ND 98.69 200 mg (1:3.25) pH5.0 + lactose ND 0.04 0.87 ND ND 98.64 300 mg (1:4.87)

TABLE 6b Epi- mer Tigecy- Sample ID RRT 0.5 0.55 0.74 1.25 1.67 cline(molar ratio) MW 601 583 585 528 556 585 pH 5.0 no lactose 0.03 0.075.40 0.02 0.07 94.19 pH 5.0 + lactose 0.02 0.04 3.83 0.01 0.05 95.87 15mg(1:0.24) pH 5.0 + lactose 0.01 0.03 3.02 ND 0.03 96.72 31 mg(1:0.50)pH 5.0 + lactose 0.01 0.03 2.18 ND 0.02 97.61 62 mg (1:1.00)

What is claimed is:
 1. A composition consisting of tigecycline, lactose,and an acid, wherein the molar ratio of tigecycline to lactose isbetween about 1:1.6 to about 1:3.3, and the pH of the composition in asolution is between about 4.0 and about 5.0, wherein the acid ishydrochloric acid, and the composition further comprises tigecyclineepimer in an amount that is not more than 2.56% as measured afterstorage of the composition at about 40° C. and 75% relative humidity fornot more 39 days.
 2. The composition of claim 1, wherein the compositionis lyophilized.
 3. The composition according to claim 1 furthercomprising a pharmaceutically acceptable diluent.
 4. The compositionaccording to claim 3, wherein the pharmaceutically acceptable diluent iswater, a saline, Lactated Ringer's Injection solution, or dextrosesolution.
 5. The composition of claim 1, wherein the pH of thecomposition in a solution is between 4.2 and about 4.8.
 6. A compositionprepared in accord with a process comprising combining lactose withtigecycline and water to form a solution; reducing the pH of thesolution with hydrochloric acid to between about 4.0 and about 5.0; andlyophilizing the solution to dryness to prepare a lyophilizedcomposition; wherein the lactose is capable of reducing epimer formationof tigecycline whereby the lyophilized composition further comprisestigecycline epimer in an amount that is not more than 2.56% as measuredafter storage of the lyophilized composition at about 40° C. and 75%relative humidity for not more 39 days, and the molar ratio oftigecycline to lactose is between about 1:1.6 to about 1:3.3.
 7. Thecomposition of claim 6 further comprising combining the composition witha saline, Lactated Ringer's Injection solution or dextrose solution. 8.The composition of claim 6, wherein a solid is formed.
 9. Thecomposition of claim 6, wherein the pH of the solution is reduced tobetween about 4.2 and about 4.8.